The invention relates to dialed number validation and, more particularly, to the validation of dialing plans within a system that complies with the ANSI 41, revision C, standard for cellular radiotelecommunications intersystem operations.
Mobile cellular radiotelecommunications systems (cellular systems hereinafter) have evolved to permit the continuous operation of a cellular telephone as the telephone""s subscriber roams from cell to cell and across system boundaries. Mobile communications in the telephony industry generally comply with a standard adopted and recognized by the American National Standards Institute (ANSI), referred to as ANSI 41. The ANSI 41 standard is published by the Telecommunications Industry Association/Electronics Industry Association (TIA/EIA) TR-45.2 subcommittee, and is hereby incorporated by reference. Although ANSI 41 has evolved to incorporate additional features over the years, an essential aspect of any cellular system, dialed number validation, has not been directly addressed by the standard. Dialed number validation is the process of determining whether a dialed number is allowable for a particular subscriber. Dialed number validation typically includes such steps as determining that a set of dialed digits contains the correct number of digits and that the serving switch can translate the digits and route the call. Validation could also include per subscriber information such as a list of digit strings that a subscriber may be allowed to use or geographic-based and time-based restrictions.
In today""s cellular networks, dialed number validation is typically performed at the serving mobile switching center. Hence, each mobile switching center must contain the necessary data to perform this function for each subscriber that it serves. (Because metropolitan areas are covered by multiple mobile switching centers and because many networks extend nationwide, there is extensive duplication of this data throughout the network.) In addition, a subscriber""s home location register typically contains some dialing plan-related functionality such as classes of service and allowable features. These capabilities are passed to the visited location register during normal ANSI 41 processing such as profile transfer. The serving mobile switching center then uses the combination of its translations and the visited location register to process call originations. In addition, the serving mobile switching center may use Wireless Intelligent Network (WIN) capabilities to request further translation of dialed digits from other network nodes.
However, there are various call scenarios in which dialed number validation is required and it is either not possible to perform the function at the serving node or it would require extensive duplication of translation information. There is no operation defined in ANSI 41 for dialed number validation. This invention provides a means of doing so.
As an example, if a subscriber travels from his home mobile cellular system in Boston to a different system in New York, and the subscriber wants to update his call forward-to number, the subscriber must enter a specific sequence of digits to invoke this feature. His home systems in Boston and his visited system in New York may use different digit sequences to invoke this feature. Nevertheless, it is highly desirable that all the features the subscriber pays for in his home system are available to him in all systems in which he might travel. One approach to providing this xe2x80x9cseamlessxe2x80x9d transfer of service would involve duplicating all the subscriber""s cellular system information, including his dialing plan information, at each mobile switching center the subscriber visits. However, this approach is impractical because duplicating this information for every subscriber at every mobile switching center would impose a significant burden on the storage, processing, and maintenance requirements of mobile cellular systems.
Rather than copying complete subscriber information for each subscriber to each system network element, conventional systems typically use the ANSI 41 Feature Request capability to get validation of the request and update the data at the home location register; specifically, xe2x80x9cis the mobile allowed to use the call forwarding feature?xe2x80x9d and xe2x80x9cis the forward-to number valid?xe2x80x9d However, since ANSI 41 does not define a procedure for inter-system dialed number validation, this requires the home location register to have a copy of the mobile""s dialed number translations.
In addition to such feature scenarios, other cases where inter-system dialed number validation could be used include node-based services where calls are originated on behalf of a mobile subscriber such as voice-based dialing applications or callback capabilities on voicemail systems. In these situations, a mobile originated call is routed to an adjunct system which queries the mobile for dialed digits and subsequently routes the call out to the network. Instead of duplicating the dialed number translations which reside on the mobile switching centers, the adjunct could invoke a dialed number validation request prior to routing.
Another potential application of dialed number validation capability is in the centralization of dialing plan functionality. Although the processing and signaling overhead of per-call inter-system validation would be potentially onerous today (and could be accomplished in part using WIN capabilities), it is envisioned that all or part of dialing plans could be centralized and accessed at various points, or from various network elements, during the processing of a mobile call (currently not supported by WIN).
A system and method that conform to the ANSI 41 standard and that provide dialed number validation between nodes in a cellular system would therefore be particularly desirable.
A cellular system in accordance with the principles of the present invention permits one node, or a network element, within a cellular network to request validation information from a network element in another cellular system.
In an illustrative embodiment, when a subscriber keys in digits in his mobile cellular unit that invoke the call forwarding feature with a forward-to number, the serving mobile switching center sends a feature request message to the subscriber""s home location register. The home location register determines that the mobile user has access to the feature and then sends an ANSI 41-compliant dialed number validation request message to the subscriber""s home mobile switching center in order to determine whether the dialed digits keyed in by the subscriber are allowed under the subscriber""s dialing plan. After making the determination, the home mobile switching center returns a message to the home location register that indicates whether the digits keyed in by the subscriber are allowed according to his dialing plan. The home location register then updates the forward-to number for the subscriber and returns a feature request return result to the serving mobile switching center, indicating whether the feature request was successfully processed.
Various network elements, including visited mobile switching centers, home mobile switching centers, home location registers, service control points, and service nodes may initiate and complete the new dialed number validation request.